The primary aim of this study was to determine changes in CI and SI, if any, in children hospitalized with status asthmatics during the course of treatment as measured by non-invasive EC monitoring. The secondary aim was to determine if there is an association between Abnormal CI (defined as <5 or >95 % tile adjusted for age) and Abnormal ECG (defined as ST waves changes) Non-invasive cardiac output (CO) recordings were obtained daily from admission (Initial) to discharge (Final). Changes in CI and SI measurements were compared using paired t tests or 1-way ANOVA. The association between Abnormal CI on Initial CO recording and Abnormal ECG was analyzed by Fischer's exact test. Data are presented as mean ± SEM with mean differences reported with 95 % confidence interval; p < 0.05 was considered significant. Thirty-five children with critical asthma were analyzed. CI decreased from 6.2 ± 0.2 to 4.5 ± 0.1 [-1.6 (-0.04 to -0.37)] L/min/m(2) during hospitalization. There was no change in SI. There was a significant association between Abnormal Initial CI and Abnormal ECG (p = 0.02). In 11 children requiring prolonged hospitalization CI significantly decreased from 7.2 ± 0.5 to 4.0 ± 0.2 [-3.2 (-4.0 to -2.3)] L/min/m(2) and SI decreased from 51.2 ± 3.8 to 40.3 ± 2.0 [-11.0 (-17.6 to -4.4)] ml/beat/m(2) There was a significant decrease in CI in all children treated for critical asthma. In children that required a prolonged course of treatment, there was also a significant decrease in SI. Abnormal CI at Initial CO recording was associated with ST waves changes on ECG during hospitalization. Future studies are required to determine whether non-invasive CO monitoring can predict which patients are at risk for developing abnormal ECG.